1. Field of the Invention
The present invention relates to an arteriosclerosis inspecting apparatus for inspecting arteriosclerosis of a living subject based on an augmentation index or pulse-wave-velocity-related information.
2. Related Art Statement
A degree of arteriosclerosis of a living subject can be evaluated based on augmentation index AI or pulse-wave velocity PWV each as a parameter that is related to artery's degree of elasticity or dilation.
A pulse wave that propagates through an artery of the subject is reflected at a bifurcated or tapered portion of the artery. Therefore, a shape or form of the pulse wave detected from the artery is defined by the composition of an incident-wave component that is produced when blood is ejected from the heart of the subject and advances toward a peripheral portion of the subject, and a reflected-wave component that is produced when the incident-wave component is reflected. Thus, augmentation index AI is obtained by determining a proportion of a reflected-wave component of a pulse wave detected from an artery, such as a carotid artery or a brachial artery, to an incident-wave component of the detected pulse wave. As the artery hardens, phase or amplitude of the reflected-wave component changes. Usually, augmentation index AI is calculated as a percentage of a value obtained by dividing a difference between a magnitude of the detected pulse wave at the time of detection of a peak point of the reflected-wave component and a magnitude of the detected pulse wave at the time of detection of a peak point of the incident-wave component, by a pulse pressure of the detected pulse wave.
Pulse-wave velocity PWV is calculated based on a time difference DT between respective pulse waves detected from two portions of the artery of the subject that are located at different distances from the heart of the subject, and a distance difference DL between the respective distances of those portions from the heart. As the artery hardens, the pulse-wave velocity PWV increases. Usually, the pulse-wave velocity PWV is calculated by dividing the distance difference DL by the time difference DT.
Meanwhile, the form of pulse wave is influenced by not only arteriosclerosis but also various other factors such as blood pressure. Therefore, augmentation index AI may be influenced by cardiac output or afterload, and accordingly it is difficult to diagnose arteriosclerosis based on this index AI only. Thus, the index AI has been used in only cases where a specialist having experience and knowledge uses it.
In addition, since pulse-wave velocity PWV depends on blood pressure, it cannot be used solely. Thus, respective measured values of augmentation index and pulse-wave velocity are used in combination to diagnose a degree of hardening of artery. However, in the case where pulse-wave velocity PWV lowers because of blood-pressure decrease caused by arteriostenosis, or because of aneurysm, it is possible to make an erroneous diagnosis about arteriosclerosis. In addition, in the case where an antihypertensive agent is administered to a hypertensive patient to lower blood pressure of the patient to a normal range and thereby lower pulse-wave velocity PWV of the patient to below a standard value, it is difficult to judge whether arteriosclerosis of the patient has been really improved.